This application is a 35 USC 371 application of PCT/DE 00/02734 filed on Aug. 12, 2000.
1. Field of the Invention
The invention relates to a fuel injection valve having a valve body, which contains a movable injector needle, an having actuating part, which supports the injector needle and communicates with a control pressure chamber, and having a compensation chamber, which communicates with a compensation piston.
2. Description of the Prior Art
A fuel injection valve of the type with which this invention is concerned has been disclosed by DE 197 27 896 A1. In this known valve, the compensation chamber is used to compensate for an opening force which acts on the injector needle after it opens. This occurs because when the injector needle lifts up from its valve seat, an additional area is acted on by high-pressure so that forces that increase up to a limit value act on the injector needle in the opening direction. In order to compensate for the opening force, a compensating force which counteracts the opening force is produced in the compensation chamber. In the known fuel injection valve, the actuating part is provided with an annular shoulder that is disposed inside the compensation chamber. The compensation chamber is filled with a fluid, for example the fuel to be injected, so that a hydraulic chamber is produced which is closed but whose volume can be displaced by the movement of the compensation piston. When the injector needle is open, the actuating part is pushed further into the compensation chamber so that because of the annular shoulder, the fuel in the compensation chamber is displaced. This displacement initially produces a pressure increase in the compensation chamber due to the rigidity of the hydraulic volume and the elastic properties of the fuel contained therein. After this initial pressure increase, the volume of the compensation chamber is displaced as a result of which the compensation piston is also moved. The force counteracting this movement acts as a closing force on the actuating member. The progression and amount of closing force can be adjusted by means of the volume of the compensation chamber and the embodiment and impingement of the compensation piston.
The fuel injection valve according to the invention has the advantage that the compensating force can be produced in a simpler manner without the need for a hydraulic chamber between the actuating part and the compensation piston. In particular, this eliminates all the problems that stem from the use of a hydraulic fluid, namely supplying the hydraulic fluid and preventing unintentional escape of the hydraulic fluid.
According to a preferred embodiment of the invention, the spring element is constituted by at least one Belleville washer, or disk spring. A disk spring or a disk spring packet has the advantage that it produces a characteristic curve which, in a particular range, demonstrates a very small increase in the spring force over the spring travel. As a result, an essentially constant closing force can be produced.
According to a preferred embodiment of the invention, the compensation piston is disposed concentric to the longitudinal axis of the actuating part. This produces a particularly compact design of the fuel injection valve.
According to one variant, the compensation piston is annular and encompasses the actuating part, the compensation chamber is an annular chamber which encompasses the actuating part and is closed at one end by the compensation piston, and the actuating part is provided with a collar which supports the spring. This embodiment produces a design of the fuel injection valve that is very compact in the axial direction.
According to another variant, at the end remote from the injector needle, the actuating part is provided with a support disk, which supports the spring, and the support disk is disposed opposite from the compensation piston which, at its end remote from the injector needle, is provided with an extension that closes one end of the compensation chamber. This embodiment produces a design of the fuel injection valve that is slender in the radial direction.
Preferably, two stops for the compensation piston are embodied on the valve body, which determine the end positions of the compensation piston. Consequently, in the event of an excessively high or excessively low pressure in the compensation volume, there are preset positions the compensation piston which assure a correct operation of the fuel injection valve.